This invention relates to the measurement of the gas and water content in oil, particularly crude oil.
Where crude oil is being pumped from the ground it is generally desirable to be able to measure its gas and water content.
In the past a number of methods of measuring the gas and water content of crude oil have been proposed. These generally fall into two groups, the first being methods where a sample of the oil flow is taken and the sample is analysed and the other being so called full flow systems where the aggregate gas and water content of the entire flow is measured.
In general measurements involving sampling have been unpopular because the gas and water content of the oil flow is non-homogenous over time or across the width of a pipe so there is no guarantee that a sample is representative unless a homogenizer is used to homogenize the gas, oil and water in the flow. Generally speaking homogenizers are not completely effective and require power to operate them. The need for such power supply can be a considerable problem in under sea applications but the main problem with systems of this type is the difficulty of ensuring that a sample is fully representative of the gas and water content of the oil flow as a whole, even when a homogenizer is used.
As a result, full flow systems are preferred. One method of carrying out full flow measurement which has been proposed is the use of microwave energy. If microwave energy is passed through a mixture of water, oil and gas it is possible to deduce the proportions of the flow made up of the three constituents by measuring the attenuation of the microwave energy. This is possible because oil, water and gas have very different permitivities.
Theoretically, such a calculation would be extremely simple if the flow of oil, gas and water was homogeneous. However, as explained above, it generally is not homogeneous, and as a result, in practice, it has proved extremely difficult to relate the changes in permitivity measured by microwave absorption systems to the actual proportions of water and gas in the oil flow.